U.S. patent application number 15/767506 was filed with the patent office on 2018-10-11 for method for forming a three dimensional body from a mixture with a high content of solid particles.
The applicant listed for this patent is SAINT-GOBAIN CERAMICS & PLASTICS, INC.. Invention is credited to Matthew GACEK, Bojana LANTE, Jean-Marie LEBRUN, Paul W. REHRIG, Michael SENDER.
Application Number | 20180290380 15/767506 |
Document ID | / |
Family ID | 58518423 |
Filed Date | 2018-10-11 |
United States Patent
Application |
20180290380 |
Kind Code |
A1 |
REHRIG; Paul W. ; et
al. |
October 11, 2018 |
METHOD FOR FORMING A THREE DIMENSIONAL BODY FROM A MIXTURE WITH A
HIGH CONTENT OF SOLID PARTICLES
Abstract
A method for continuously forming a three-dimensional body from
a mixture, the mixture comprising at least 15 vol % solid particles
and a radiation curable material. The method allows the continuous
production of three-dimensional bodies comprising to a high content
ceramic particles at a forming speed of at least 25 mm/hour.
Inventors: |
REHRIG; Paul W.; (Sterling,
MA) ; GACEK; Matthew; (Rutland, MA) ; LANTE;
Bojana; (Northborough, MA) ; SENDER; Michael;
(Cambridge, MA) ; LEBRUN; Jean-Marie;
(Marlborough, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAINT-GOBAIN CERAMICS & PLASTICS, INC. |
Worcester |
MA |
US |
|
|
Family ID: |
58518423 |
Appl. No.: |
15/767506 |
Filed: |
October 14, 2016 |
PCT Filed: |
October 14, 2016 |
PCT NO: |
PCT/US2016/057061 |
371 Date: |
April 11, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62242150 |
Oct 15, 2015 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 2235/6565 20130101;
C04B 2235/782 20130101; C04B 35/486 20130101; C04B 2235/77
20130101; B29C 64/264 20170801; B29C 2035/0827 20130101; C04B
35/584 20130101; C04B 2235/94 20130101; B29C 70/58 20130101; B29C
64/135 20170801; C04B 2235/786 20130101; C04B 35/6269 20130101;
B29C 64/165 20170801; C04B 2235/5436 20130101; B33Y 70/00 20141201;
C04B 35/14 20130101; C04B 2235/9615 20130101; C04B 2235/5409
20130101; C04B 35/632 20130101; C04B 2235/5445 20130101; B29C
64/129 20170801; C04B 2235/6562 20130101; C04B 35/111 20130101;
C04B 35/565 20130101; C04B 35/6263 20130101; C04B 2235/6026
20130101; C04B 35/64 20130101; C04B 35/443 20130101; C04B 35/6264
20130101; B33Y 10/00 20141201; B28B 1/001 20130101; B29C 35/0805
20130101 |
International
Class: |
B29C 64/165 20060101
B29C064/165; B28B 1/00 20060101 B28B001/00; C04B 35/64 20060101
C04B035/64; B29C 35/08 20060101 B29C035/08 |
Claims
1. A method of forming a body comprising: forming a
three-dimensional body from a mixture, the mixture comprising at
least 15 vol % of solid particles for a total volume of the mixture
and a radiation-curable material, wherein forming includes
continuous translation and growth of the body from an interface of
the mixture.
2. A method of forming a body comprising: providing an assembly
including a chamber containing a mixture and a construction;
forming a three-dimensional body by continuously creating and
attaching a radiation cured translating portion to a carrier plate
of the construction and increasing a distance between the carrier
plate and the mixture in a continuous manner to create a
three-dimensional body within the mixture, wherein during forming
the three-dimensional body is adjacent to an interface of an
inhibition zone of the mixture, wherein the mixture comprises a
liquid characteristic selected from the group of: a shear-thinning
slurry; a shear-thinning slurry with a radiation-curable material;
a content of solid particles of at least 15 vol % for a total
volume of the mixture; a yield point of less than 10 Pa; a
viscosity of at least 50 cP at a shear rate of less than about 5
Hz, and a viscosity of less than 1000 cP at a shear rate greater
than about 25 Hz; or a combination thereof.
3. The method of claim 1, wherein the radiation-curable material
comprises a photoinitiator and a polymerizable monomer.
4. The method of claim 1, wherein during forming portions of the
mixture are subjected to electromagnetic radiation having a
wavelength in a range from 200 nm to 760 nm.
5. The method of claim 4, wherein the electromagnetic radiation has
a wavelength from at least 370 nm to not greater than 450 nm.
6. The method of claim 4, wherein the electromagnetic radiation has
an energy from at least 20 mJ/cm.sup.2 to not greater than 450
mJ/cm.sup.2.
7. The method of claim 1, wherein the solid particles include
ceramic particles, metallic particles, polymeric particles, or any
combination thereof.
8. The method of claim 7, wherein the solid particles are selected
from the group of alumina, silica, MMA, or zirconia.
9. The method of claim 4, wherein the applied electromagnetic
radiation has a power of at least 0.1 mW/cm.sup.2 and not greater
than 250 mW/cm.sup.2.
10. The method of claim 1, wherein the mixture is a shear thinning
slurry.
11. The method of claim 1, wherein forming is conducted at a
forming speed of at least 25 mm/hr.
12. The method of claim 11, wherein forming is conducted at a
forming speed of at least 60 mm/hr.
13. A method of forming a body comprising: forming a
three-dimensional body using an additive manufacturing process, the
three-dimensional body having a content of ceramic solid particles
of at least 15 vol % for a total volume of the three-dimensional
body, wherein the three-dimensional body has a total volume of at
least 0.1 mm.sup.3, and wherein forming is completed at a forming
speed of at least 25 mm/hr.
14. The method of claim 13, wherein the forming speed is at least
60 mm/hr.
15. The method of claim 13, further comprising high temperature
sintering of the three-dimensional body at a temperature of at
least 1000.degree. C.
16. The method of claim 2, wherein the radiation-curable material
comprises a photoinitiator and a polymerizable monomer.
17. The method of claim 2, wherein the electromagnetic radiation
has a wavelength from at least 370 nm to not greater than 450
nm.
18. The method of claim 2, wherein the solid particles include
ceramic particles, metallic particles, polymeric particles, or any
combination thereof.
19. The method of claim 2, wherein the mixture is a shear thinning
slurry.
20. The method of claim 2, wherein forming is conducted at a
forming speed of at least 25 mm/hr.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a method for continuously
forming a three-dimensional body from a mixture, the mixture
comprising solid particles and a radiation curable material.
BACKGROUND ART
[0002] The manufacturing of polymeric three-dimensional bodies
based on a layer by layer built up of a radiation curable liquid
material has become of increasing interest, especially in view of
the enhancement in production speed if a bottom-up technique is
employed.
[0003] Although it is known that ceramic bodies may also be
manufactured via a layer by layer construction of radiation curable
ceramic slurries, the production speed for making these materials
is still very slow and improvement of the uniformity, density and
strength of manufactured ceramic bodies is desirable. The
manufacturing of complex three dimensional structures including
ceramic can find applications in a wide range of fields, for
example, in the automotive and aerospace industry, or in medicine
for the making of custom implants and dental models.
SUMMARY
[0004] According to one embodiment, a method of forming a body
comprises forming a three-dimensional body from a mixture, the
mixture comprising at least 15 vol % of solid particles for a total
volume of the mixture and a radiation-curable material, wherein
forming includes continuous translation and growth of the body from
an interface of the mixture.
[0005] According to another embodiment, a method of forming a body
comprises providing an assembly including a chamber containing a
mixture and a construction; forming a three-dimensional body by
continuously creating and attaching a radiation cured translating
portion to a carrier plate of the construction and increasing a
distance between the carrier plate and the mixture in a continuous
manner to create a three-dimensional body within the mixture,
wherein during forming the three-dimensional body is adjacent to an
interface of an inhibition zone of the mixture. The mixture
comprises a mixture characteristic selected from the group of a
shear-thinning slurry; a shear-thinning slurry with a
radiation-curable material; a content of solid particles of at
least 15 vol % for a total volume of the mixture; a yield point of
less than 10 Pa; a viscosity of at least 50 cP at a shear rate of
less than about 5 Hz, and a viscosity of less than 1000 cP at a
shear rate greater than about 25 Hz; or a combination thereof.
[0006] According to a further embodiment, a method of forming a
body comprises forming a three-dimensional body using an additive
manufacturing process, the three-dimensional body having a content
of ceramic particles of at least 15 vol % for a total volume of the
three-dimensional body, wherein the three-dimensional body has a
total volume of at least 0.1 mm.sup.3, and wherein creating is
completed at a rate of at least 25 mm/hr.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The present disclosure may be better understood, and its
numerous features and advantages made apparent to those skilled in
the art by referencing the accompanying drawings.
[0008] FIG. 1A includes an illustration of an assembly according to
one embodiment, showing the starting phase of forming of a
three-dimensional body.
[0009] FIG. 1B includes an illustration of an assembly according to
one embodiment, showing a later phase of forming of a
three-dimensional body.
[0010] FIG. 2A includes an illustration of a bottom portion of the
assembly according to one embodiment.
[0011] FIG. 2B includes an illustration of a bottom portion of the
assembly according to an embodiment.
[0012] FIG. 3 is a graph showing the cure depth with increasing UV
exposure of mixtures containing each a different type of ceramic
particles and of a mixture without ceramic particles.
[0013] FIG. 4 is a graph showing the thickness of the inhibition
zone in dependence to the UV exposure of a mixture containing
ceramic particles according to one embodiment and of a mixture
without ceramic particles.
[0014] FIG. 5 is a graph comparing two types of oxygen permeable
membranes with regard to the thickness of an inhibition zone formed
during varying UV exposure according to embodiments.
[0015] FIG. 6 is an image of a continuously formed
three-dimensional green body comprising alumina particles according
to one embodiment.
[0016] FIG. 7 is an image comparing continuously formed
three-dimensional green bodies comprising alumina particles
according to embodiments.
[0017] FIG. 8A is an image of a continuously formed green body
comprising alumina particles according to one embodiment.
[0018] FIG. 8B is an image of a continuously formed green body
comprising alumina particles as a comparative example.
[0019] FIG. 9 is an image of a continuously formed green body
comprising silica particles according to one embodiment.
[0020] FIG. 10A is an image of a magnified surface structure of a
continuously formed green body comprising MMA particles according
to one embodiment.
[0021] FIG. 10 B is an image of a magnified surface structure of a
continuously formed green body comprising MMA particles as a
comparative example.
[0022] FIG. 11 is an image of a continuously formed
three-dimensional green body comprising zirconia particles
according to one embodiment.
[0023] FIG. 12 is a graph comparing cure depth with increasing UV
exposure of mixtures with different amounts of silica
particles.
[0024] FIG. 13 is a graph comparing viscosity with increasing shear
rate of mixtures with different amounts of silica particles.
[0025] FIG. 14 is an image comparing continuously formed
three-dimensional green bodies from mixtures with different silica
content.
[0026] FIG. 15 is a graph comparing cure depth with increasing UV
exposure of mixtures with different alumina particle sizes.
[0027] FIG. 16 is a graph comparing viscosity with increasing shear
rate of mixtures with different alumina particle sizes.
[0028] FIG. 17A is an image of a continuously formed flower shaped
green body comprising alumina particles according to one
embodiment.
[0029] FIG. 17B is an image of a continuously formed flower shaped
ceramic body after high temperature sintering according to one
embodiment.
[0030] FIG. 18 is an image of a polished cross-section of an
individual post of the flower shaped ceramic body of FIG. 17B after
high temperature sintering according to one embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0031] As used herein, the terms "comprises," "comprising,"
"includes," "including," "has," "having" or any other variation
thereof, are intended to cover a non-exclusive inclusion. For
example, a process, method, article, or apparatus that comprises a
list of features is not necessarily limited only to those features
but may include other features not expressly listed or inherent to
such process, method, article, or apparatus.
[0032] As used herein, and unless expressly stated to the contrary,
"or" refers to an inclusive-or and not to an exclusive-or. For
example, a condition A or B is satisfied by any one of the
following: A is true (or present) and B is false (or not present),
A is false (or not present) and B is true (or present), and both A
and B are true (or present).
[0033] Also, the use of "a" or "an" are employed to describe
elements and components described herein. This is done merely for
convenience and to give a general sense of the scope of the
invention. This description should be read to include one or at
least one and the singular also includes the plural unless it is
obvious that it is meant otherwise.
[0034] As used herein, the term mixture refers to a fluid of a
certain viscosity, including a liquid component and solid
particles. The liquid component may include a radiation curable
material.
[0035] As used herein, the term three dimensional body refers to a
body containing radiation cured resin and at least 15 vol % solid
particles based on the total volume of three dimensional body. In
the embodiments that the solid particles are ceramic particles, the
three dimensional body is also called green body as a synonymous
expression, as long it is before the stage of high temperature
sintering (before removal of the cured resin).
[0036] Various embodiments of the present disclosure will now be
described, by way of example only, with reference to the
accompanying drawings.
[0037] The present disclosure relates to a method of continuously
forming a three-dimensional body from a mixture. The mixture can
comprise solid particles in an amount of at least 15 vol % and a
liquid radiation-curable material, wherein the forming includes
continuous translation and growth of the three-dimensional body
from an interface of the mixture.
[0038] The method includes providing an assembly designed for
working with radiation curable mixtures containing a particular
concentration of solid particles. As demonstrated in the embodiment
shown in FIG. 1A, the assembly can have a computer controlled
electromagnetic radiation unit (11), a chamber (12), and a
construction unit (13). The electromagnetic radiation unit (11) can
include a UV or visible light (14) emitting radiation source, for
example, a laser or a light emitting diode (led) and may project a
varying CAD/CAM created two-dimensional image onto a transparent
window (15) at the bottom of the chamber (12). The chamber (12) can
include a mixture (16) that can include a radiation curable
material and solid particles. The transparent window (15) of the
chamber can also be semipermeable for an inhibitor gas or may
include an additional semipermeable layer (not shown) for the
penetration of an inhibitor, for example oxygen, into the mixture
(16) of the chamber (12). During the forming process, the inhibitor
may enter the chamber (12) by permeating the transparent window
(15) and form an inhibition zone (17) at a bottom region of the
mixture (16). In the inhibition zone (17) the inhibitor can limit
or prevent curing of the mixture (16) by the electromagnetic
radiation.
[0039] According to one embodiment, a carrier plate (18) can be
positioned above the chamber (12). The position between the carrier
plate (18) and the mixture in the chamber (12) can be changed
during the forming process to facilitate formation of the
three-dimensional body. When the formation of the three-dimensional
body is started, the carrier plate (18) can be emerged into the
mixture (16) up to a pre-calculated distance from the interface of
the inhibition zone (22). According to one embodiment, the
pre-calculated distance corresponds to a portion of the mixture
that can be radiation cured (translated from liquid to solid state)
if subjected to electromagnetic radiation from the radiation unit
(11) underneath the chamber (12), and is furtheron called
"translating portion" (19). The radiation cured translating portion
(19) can adhere to the carrier plate (18) and be vertically moved
away from the interface of the inhibition zone (22). Concurrently
with the upwards movements of the carrier plate (18) and the
attached solidified translating portion (19), mixture (16) from the
sides of the polymerization chamber or from a reservoir (20) can
fill the released space. The construction is designed to move the
carrier plate (18) continuously upwards in z direction at a speed
that corresponds to the time needed for radiation curing mixture
(16) that replaces the upwards moved solidified translating
portion.
[0040] FIG. 1B demonstrates an embodiment including a partially
formed three-dimensional body (21) having three solidified and
unified translating portions and one translating portion (19) which
is subjected to radiation curing and attached to the
three-dimensional body (21).
[0041] The increase in distance between the carrier plate (18) and
the mixture (16) when forming the three-dimensional body (21) can
be caused by moving either the carrier plate (18) or the chamber
(12) or both carrier plate (18) and chamber (12) in relation to
each other.
[0042] The carrier plate (18) of the assembly of the present
disclosure is configured for continuous movement to facilitate
formation of the three-dimensional body away from the interface of
the inhibition zone (22). As used herein, the phrase "interphase of
the inhibition zone" (22) can be used interchangeable with the
phrase "interface of the mixture," since the inhibition zone is a
zone of the mixture, which only distinguishes from the other part
of the mixture by the presence of an inhibitor in a concentration
that the mixture may not cure if exposed to electromagnetic
radiation. Actual solidification and forming of the three
dimensional body starts at the interface of the inhibition zone
(22), i.e., an interface of the mixture.
[0043] The formation of the three dimensional body may not
necessarily be considered a layer-by-layer forming process.
Instead, the forming process (e.g., curing) may be in the form of a
gradient of solidification (e.g., polymerization). The processes of
the embodiments herein may facilitate formation of a
three-dimensional body having smoother features and may have
improved mechanical properties, compared to conventional structures
formed by layer-by-layer forming processes.
[0044] As used in the context of the present disclosure, continuous
translation and growth of the three-dimensional body means that the
carrier plate (18) can be moved in a continuous manner or in
discrete steps with short stops between each step, as long the
stops allow that a gradient of solidification is maintained while
forming the three-dimensional body. A gradient of solidification
means that especially in the translating portion (19) a continuous
polymerization reaction is maintained, with the highest degree of
solidification at the farthest distance to the inhibition zone. The
three-dimensional body formed by the process of continuous
translation can thereby possess a non-layered internal structure,
such that in a crosscut along the z-axis, changes in the morphology
of the green body are not visible to the naked eye. In comparison,
traditional layer by layer build-up of a green body waits until one
layer is completely radiation cured before the next layer is
applied, which leaves visible cleavage lines in the formed green
body, i.e., regions that are not smoothly connected together.
[0045] In embodiments, the stops in the movement of the carrier
plate (18) while conducting continuous translation and forming of
the three-dimensional body can be at least 1 microsecond, such as
at least 300 microseconds, at least 500 microseconds, at least 800
microseconds, or at least 1000 microseconds. In other embodiments,
the stops during continuous translation may be not longer that 1
second, such as not longer than 0.5 seconds, not longer than 0.3
seconds, not longer than 0.2 seconds, or not longer than 0.1
seconds. It will be appreciated that the stops during continuous
translation can be a value within any of the minimum and maximum
values note above, such as from 1 microsecond to 1 second, from 300
microseconds to 0.5 seconds, or from 1000 microseconds to 0.1
seconds.
[0046] In further embodiments, the method of the present disclosure
can also include one or more longer stops during the forming of the
three-dimensional body, such that the gradient of solidification
may be interrupted and the translation is not continuous as defined
above. Such longer stops may be desired for the making of a body
having defined regions which are cleavable.
[0047] The cure depth of the electromagnetic radiation (14) applied
to the mixture (16) may be effected by the size, type, and
concentration of the solid particles and the refractive index of
the particle slurry. Notably, the size and concentration of the
solid particles may be particularly selected to facilitate proper
operation of the process in combination with the type of
electromagnetic radiation used for the curing process.
[0048] According to an embodiment, suitable formation of a
three-dimensional body having a suitable strength, can include
controlling the cure depth relative to a thickness of the
translating portion. In one embodiment, the cure depth may be at
least 25% larger than the thickness of the translating portion
(19), such as at least 30%, at least 35%, or at least 40%. In
another embodiment, the cure depth can be not greater than 75% of
the thickness of the translating portion (19), such as not greater
than 70% or not greater than 65%. It will be appreciated that the
cure depth can be a value between any of the maximum and minimum
values noted above, such as from 25% to 75%, from 30% to 70% or
from 35% to 60% of the thickness of the translating portion
(19).
[0049] In one embodiment, a thickness of the translating portion
(19) can be at least 50 .mu.m, such as at least 70 .mu.m, or at
least 100 .mu.m. In another embodiment, the thickness of the
translating portion may be not greater than 500 .mu.m, such as not
greater than 450 .mu.m, or not greater than 400 .mu.m. It will be
appreciated that the thickness of the translating portion can be a
value between any of the maximum and minimum values note above,
such as from 50 .mu.m to 500 .mu.m, from 80 .mu.m to 450 .mu.m, or
from 100 .mu.m to 300 .mu.m.
[0050] In a further aspect, the cure depth may be at least 1 .mu.m
larger than the thickness of the inhibition zone (17), such as at
least 5 .mu.m, at least 10 .mu.m, at least 20 .mu.m, or at least 50
.mu.m larger than the thickness of the inhibition zone. In yet
another aspect, the cure depth can be not greater than 400 .mu.m
than the thickness of the inhibition zone, such as not greater than
350 .mu.m, not greater than 300 .mu.m, or not greater than 250
.mu.m than the thickness of the inhibition zone. It will be
appreciated that the cure depth can be a value between any of the
maximum and minimum values noted above, such as within a range of
at least 1 .mu.m to not greater than 400 .mu.m, from 5 .mu.m to 370
.mu.m, or from 30 .mu.m to 300 .mu.m larger than the thickness of
the inhibition zone.
[0051] The thickness of the inhibition zone (17), which can be
formed when the inhibitor enters the chamber (12) through the
transparent and semipermeable window, (15) may be regulated by the
concentration of the inhibitor. The inhibition zone (17) may limit
the curing of the mixture (16) in that zone within the chamber
(12). The inhibition zone (17) may facilitate limited or no
adhesion of the radiation cured material to the bottom of the
chamber (12), which may further facilitate simpler release of the
body from the chamber after forming is completed.
[0052] FIGS. 2A and 2B show embodiments how a semipermeable layer
can be integrated at the bottom section of the chamber. In the
embodiment of FIG. 2A, the transparent window (24) functions also
as a semipermeable layer for the penetration of the inhibitor gas
(25), penetrating the transparent window (24) from the bottom of
the chamber. FIG. 2B shows an embodiment where an additional
semipermeable layer (26) is installed above the transparent window
(24) and the inhibitor gas (25) is provided from the sides of the
polymerization chamber.
[0053] In one embodiment, the thickness of the semipermeable layer
for the penetration of inhibitor gas can be at least about 1 .mu.m,
such as at least about 5 .mu.m, at least about 50 .mu.m, at least
about 500 .mu.m, or at least about 1000 .mu.m. The upper thickness
of the semipermeable layer may not be limited as long the layer
allows sufficient transport of inhibitor gas.
[0054] The material of the semipermeable layer may be any material
that permits the penetration of inhibitor gas. Non-limiting
examples of materials suitable for a semipermeable layer can
include, for example, fluoropolymers, such as Teflon (e.g.,
AF-2400X), polymethylpentene based membranes (PMP), or silicone
polymers and copolymers.
[0055] The inhibitor may preferably be an oxygen containing gas,
such as air, mixtures of an inert gas and oxygen, or pure oxygen.
In another aspect, when oxygen cannot inhibit the activity of the
photoinitiator (for example, when a cationic photoinitiator is
used) the inhibitor can be an amine, e.g., ammonia, ethyl amine, di
and trialkyl amines, carbon dioxide, or combinations thereof.
[0056] In one embodiment, the inhibitor can be pure oxygen, and the
oxygen may penetrate the semipermeable layer in an amount of at
least 0.1 Barrer, such as at least 1 Barrer, at least 5 Barrer, at
least 10 Barrer, or at least 30 Barrer.
[0057] The thickness of the inhibition zone should be at least in
the range of the average size of the solid particles contained in
the mixture or greater. In one embodiment, the thickness of the
inhibition zone may be at least 0.5 .mu.m, such as at least 1.0
.mu.m, at least 2.0 .mu.m, or at least 5 .mu.m. In another
embodiment, the inhibition zone may not be greater than 600 .mu.m,
such as not greater than 500 .mu.m, not greater than 300 .mu.m, or
not greater than 100 .mu.m. It will be appreciated that the
thickness of the inhibition zone can be a value between any of the
maximum and minimum values noted above, such as from 0.5 .mu.m to
600 .mu.m, from 1.0 .mu.m to 450 .mu.m, or from 3 .mu.m to 200
.mu.m.
[0058] Although the term "inhibition zone" appears to indicate that
no polymerization reaction may take place in that area of the
mixture, it will be appreciated that polymerization reactions can
also occur to a limited extent in the inhibition zone. The
inhibition zone may be also described as a gradient of
polymerization, where with increasing distance from the bottom
surface of the chamber larger amounts of polymerization reactions
can happen, but these polymerization reactions may not completely
cure the mixture, and the mixture is still maintained in a liquid
stage. The interface of the inhibition zone may be understood as
the area of the inhibition zone where the polymerization reactions
start to form a solid material.
[0059] The solid particles contained in the mixture can be any type
of inorganic or organic particles that do not dissolve in the
liquid component of the mixture under the forming conditions, and
may be uniformly distributed throughout the entire mixture. In one
aspect, the solid particles can be ceramic particles, metallic
particles, polymeric particles, or any combination thereof.
[0060] In a particular embodiment, the solid particles can be
ceramic particles, such as an oxide, a carbide, a boride, a
nitride, a silicide or any combination thereof. Non-limiting
examples or ceramic particles can be alumina, ceria, zirconia,
silica, magnesium-magnesia aluminate (MMA), magnesium oxide,
silicon nitride, silicon carbide, hydroxyapatite, cordierite, or
any combination thereof. In a particular embodiment, the ceramic
particles are alumina, silica, MMA, or zirconia.
[0061] The concentration of the solid particles in the mixture can
be in a range that a percolated network be formed and that the
created three-dimensional body can be densified without falling
apart upon burnout of the binder. In one embodiment, the
concentration of solid particles can be at least 15 vol %, such as
at least 16 vol %, at least 18 vol %, at least 20 vol %, at least
25 vol %, or at least 30 vol %. In another embodiment, the particle
concentration can be not greater than 80 vol %, such as not greater
than 75 vol %, not greater than 70 vol %, or not greater than 65
vol %. It will be appreciated that the concentration of solid
particles can be a value between any of the maximum and minimum
values noted above, such as from 16 vol % to 80 vol %, from 20 vol
% to 75 vol %, or from 30 vol % to 65 vol %.
[0062] The solid particles contained in the mixture can have an
average particle size of at least 0.1 .mu.m, such as at least 0.5
.mu.m, at least 1.0 .mu.m, or at least 5 .mu.m. In another aspect,
the solid particles can have an average particle size of not
greater than 20 .mu.m, such as not greater than 18 .mu.m, or not
greater than 15 .mu.m. It will be appreciated that the average size
of the solid particles can be a value between any of the maximum
and minimum values noted above, such as from 0.1 .mu.m to 20 .mu.m,
0.3 .mu.m to 18 .mu.m, or 0.5 .mu.m to 15 .mu.m.
[0063] In one embodiment, the solid particles may have a multimodal
particle distribution, for example, a bimodal or trimodal particle
distribution.
[0064] In order to provide a high quality of the formed
three-dimensional body of the present disclosure, it can be
advantageous if solid particles that exceed a certain particle size
or particles that have a size below a certain minimum be excluded.
In one embodiment, the solid particles may have a particle size
distribution wherein a value of function (d50-d10)/d50 is less than
0.8. In another embodiment, the solid particles may have a particle
size distribution wherein a value of function (d90-d50)/d50 is less
than 1.0.
[0065] In another embodiment, the solid particles contained of the
mixture may have an average particle size controlled relative to
the thickness dimension of the inhibition zone. In a preferred
aspect, an average particle size of the solid particles may not be
greater than 25% of the thickness of the inhibition zone, such as
not greater than 20%, not greater than 15%, or not greater than 10%
of the thickness of the inhibition zone.
[0066] In one embodiment, the mixture can contain at least 20 vol %
to 40 vol % ceramic particles and may be radiation cured with UV
radiation having an energy of at least 30 mJ/cm.sup.2 and not
greater than 200 mJ/cm.sup.2.
[0067] The radiation curable material contained in the mixture can
comprise polymerizable monomers, polymerizable oligomers and one or
more photoinitiators. In a preferred aspect, the radiation curable
material can contain polymerizable monomers and at least one
photoinitiator. Suitable polymerizable monomers can be, for
example, acrylates, acrylamides, urethanes, dienes, or combinations
thereof.
[0068] The photoinitiator can be a free-radical photoinitiator or a
cationic photoinitiator. In a preferred aspect, a free-radical
photoinitiator can be employed, which can be inhibited by the
presence of oxygen. Non-limiting examples of free-radical
photoinitiators can include peroxides, such as acetyl, benzoyl,
t-butyl peroxides, ketones or phosphine oxides, such as IRGACURE
819 (bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide), ESSTECH TPO
(2,4,6-trimethylbenzoyl)-phenylphosphineoxide) or a combination
thereof.
[0069] In an embodiment where a cationic photoinitiator is used,
the photopolymerization generally tends to be slower and cannot be
inhibited by oxygen. In this aspect, instead of oxygen as
inhibitor, a Bronsted acid or Lewis acid, such as metal halides and
their organometallic derivatives can be employed and released from
the bottom window of the polymerization chamber to form an
inhibition zone.
[0070] The mixture comprising the solid particles and the radiation
curable material can be subjected to electromagnetic radiation
having a wavelength in a range from 200 nm to 760 nm, depending
from the activation energy of the selected photoinitiator. In a
preferred aspect, the range of the electromagnetic radiation may be
from 370 nm to 450 nm, or from 380 nm to 410 nm.
[0071] In embodiments, the electromagnetic radiation can be created
by a laser, a light emitting diode (led), or by electron beam
radiation.
[0072] In one embodiment, the electromagnetic radiation applied for
curing the mixture can have an energy of at least 20 mJ/cm.sup.2,
such as at least 30 mJ/cm.sup.2, at least 50 mJ/cm.sup.2 or at
least 80 mJ/cm.sup.2. In another embodiment, the electromagnetic
radiation can have an energy not greater than 450 mJ/cm.sup.2, such
as not greater than 400 mJ/cm.sup.2, not greater than 350
mJ/cm.sup.2, not greater than 300 mJ/cm.sup.2, not greater than 250
mJ/cm.sup.2, not greater than 200 mJ/cm.sup.2, or not greater than
100 mJ/cm.sup.2. It will be appreciated that the electromagnetic
radiation energy can be a value between any of the maximum and
minimum values noted above, such as from 20 mJ/cm.sup.2 to 450
mJ/cm.sup.2, from 30 mJ/cm.sup.2 to 300 mJ/cm.sup.2, from 40
mJ/cm.sup.2 to 200 mJ/cm.sup.2, or from 20 to 100 mJ/cm.sup.2.
[0073] In a particular embodiment, the method of the present
disclosure may cure the mixture in the translation portion (19)
during continuous forming of the three dimensional body at a UV
power of at least 0.1 mW/cm.sup.2, such as at least 0.5
mW/cm.sup.2, at least 1.0 mW/cm.sup.2, or at least 3.0 mW/cm.sup.2.
In another particular embodiment, the applied UV power during
forming may be not greater than 250 mW/cm.sup.2, such as not
greater than 150 mW/cm.sup.2, not greater than 100 mW/cm.sup.2, not
greater than 50 mW/cm.sup.2, not greater than 30 mW/cm.sup.2, not
greater than 20 mW/cm.sup.2, not greater than 13.0 mW/cm.sup.2, not
greater than 12 mW/cm.sup.2, or not greater than 10 mW/cm.sup.2. It
will be appreciated that the applied UV power can be a value
between any of the maximum and minimum values noted above, such as
from 0.1 mW/cm.sup.2 to 250.0 mW/cm.sup.2, from 1.0 mW/cm.sup.2 to
100 mW/cm.sup.2 or from 2.0 mW/cm.sup.2 to 10 mW/cm.sup.2.
[0074] In a further embodiment, the thickness dimension of the
inhibition zone can be controlled relative to the concentration of
the solid particles. By increasing the concentration of the solid
particles, the thickness of the inhibition zone may be decreased,
as also shown in Example 2.
[0075] In another embodiment, the solid particles contained in the
mixture can include a coating overlying an exterior surface of the
particles. The coating can partially or completely cover the
surface of the solid particles. The coating may be desirable in
order to adjust the scattering and/or absorption of an applied
electromagnetic radiation in the mixture. In one aspect, the
coating can provide a 50% lower scattering of an applied
electromagnetic radiation than corresponding uncoated particles. In
a further aspect, the coating can lower the radiation scattering by
at least 55%, such as at least 60%, at least 70%, at least 80%, at
least 90% or at least 95%.
[0076] In another aspect, a coating of the solid particles can
provide a 50% lower absorbance of an applied electromagnetic
radiation absorption than corresponding uncoated particles. In
embodiments, the coating can lower the radiation absorbance in the
mixture by at least 55%, such as at least 60%, at least 65%, at
least 70%, at least 75%, at least 80%, at least 90% or at least
95%.
[0077] According to another embodiment of the present disclosure,
the mixture may include one or more additives. Non-limiting
examples of additives can be additional inhibitors to prevent
spontaneous polymerization (inert dyes), plasticizer, dispersing
agents, debinding accelerators, cross-linking monomers, pH
regulators, a pharmaceutically active ingredient, or any
combination thereof.
[0078] The rheological properties of the mixture containing solid
particles and a radiation curable material may be controlled to
facilitate suitable formation of a stable and suitably formed
three-dimensional body, including for example, a ceramic green body
having sufficient strength to be self-supporting and capable of
handling without detrimental deformation. Also, the force required
to continuously pull-up the carrier the force utilized to pull the
carrier plate away from the chamber may be adjusted based on
various parameters, including but not limited to the rheology of
the mixture.
[0079] In a particular embodiment, the mixture used for forming the
three dimensional body according to the present disclosure can be
characterized that the viscosity of the mixture decreases with
increasing shear rate. Such type of mixture is also called herein a
shear thinning slurry. In certain embodiments, the decrease of the
viscosity of the mixture from a shear rate of 0.1 s.sup.-1 to a
shear rate of 500 s.sup.-1 can be at least 10 cP, such as at least
30 cP, at least 50 cP, or at least 80 cP. In other embodiments, the
decrease in viscosity from a shear rate of 0.1 s.sup.-1 to a shear
rate of 500 s.sup.-1 may be not greater than 1500 cP, such as not
greater than 1200 cP, not greater than 1000 cP, or not greater than
800 cP. It will be appreciated that the decrease in viscosity from
a shear rate of 0.1 s.sup.-1 to a shear rate of 500 s.sup.-1 may be
a value within any of the maximum and minimum values noted above,
such as from 10 cP to 1500 cP, from 50 cP to 700 cP, or from 10 cP
to 100 cP.
[0080] In another aspect, the yield point of the mixture may be
less than 10 Pa, such as less than 8 Pa, less than 5 Pa, or less
than 3 Pa at room temperature.
[0081] In a further aspect, the mixture may have a low shear
viscosity to prevent particle settling over the duration of the
forming of the three-dimensional body. Furthermore, the solid
particles contained in the slurry may be uniformly dispersed
throughout the radiation curable material when electromagnetic
radiation is conducted such that that the three-dimensional body
can shrink uniformly during sintering. Non-uniform distribution of
the solid particles may result in undesirable macro-structural or
micro-structural features, including for example, undesirable
porosity and the like. Under low shear rate may be understood a
range of not greater about 5 Hz and at least about 0.001 Hz, with a
corresponding viscosity from at least about 50 cP to not greater
than about 5000 cP, particularly from at least 70 cP to not greater
than 1500 cP. In one aspect, the viscosity at a low shear rate of
less than about 5 Hz can be at least 100 cP.
[0082] The viscosity at a moderate to high shear rate can enable
sufficient spontaneous flow of the mixture between carrier plate
and the bottom surface of the polymerization chamber. Under
moderate to high shear rate may be understood a shear rate in a
range from at least about 25 Hz and not greater than about 3000 Hz,
with a corresponding viscosity of the mixture in a range of at
least 1 cP and not greater than 1000 cP. In one aspect, the
viscosity of the mixture at a moderate to high shear rate of
greater than 25 Hz may be less than 1000 cP.
[0083] In one embodiment, the mixture may be formed such that the
content of agglomerates of the solid particles is limited. In
certain embodiments, the mixture can be essentially free of
agglomerates of solid particles. Forming a mixture that has limited
agglomerates can include heat treatment and milling of the solid
particle powder before combining with the other components of the
mixture. In embodiments, the solid particle powder can be heat
treated at least 90.degree. C., such as at least 100.degree. C. or
even at least 105.degree. C.
[0084] Other mixing methods may be employed. The mixing process may
be controlled to control the level of agglomeration. Moreover,
over-mixing may result in degrading of the monomers and generating
too much premature polymerization of the radiation curable
resin.
[0085] In one particular embodiment, the mixture can comprise
alumina particles having an average particle size from 100 nm to
5000 nm in an amount of 15 vol % to 50 vol %.
[0086] In a certain embodiment, the alumina particles can have an
average particle size from 300 nm to 3000 nm and may be present in
an amount of 18 vol % to 40 vol %. The alumina containing mixture
may be a shear thinning slurry having a viscosity of 1 s.sup.-1 at
a shear rate of not greater than 900 cP 1, and at viscosity of at
least 70 cP at a shear rate of 500 s.sup.-1.
[0087] In another embodiment, the mixture can comprise at least 30
vol % alumina and the forming of the three dimensional body may be
conducted at an applied UV power of at least 3 mW/cm.sup.2 and not
greater than 12 mW/cm.sup.2.
[0088] In a further particular embodiment, the alumina particles
can be present the mixture in an amount of 16 vol % to 25 vol %,
and the forming of the three dimensional body may be conducted at
an applied UV power of at least 1.0 mW/cm.sup.2 and not greater
than 12 mW/cm.sup.2.
[0089] In another particular embodiment, the mixture can comprise
silica particles having an average particle size from 100 nm to
5000 nm and in an amount of 15 to 40 vol %. In a certain aspect,
the silica particles can have an average particle size from 1000 nm
to 3000 nm and may be present in an amount of 25 vol % to 35 vol %,
wherein the mixture is a shear thinning slurry having a viscosity
of not greater than 200 cP at a shear rate of 1 s.sup.-1 and a
viscosity of at least 50 cP at a shear rate of 500 s.sup.-.
[0090] In a further particular aspect, the method of the present
disclosure may employ a mixture comprising at least 25 vol %
silica, and the forming of the three dimensional body can be
conducted at an applied UV power of at least 1.0 mW/cm.sup.2 and
not greater than 12 mW/cm.sup.2.
[0091] According to an embodiment, the mixture may be essentially
free of a dye. In this embodiment, the mixture may be formed with
solid particles having the proper combination of concentration,
average particle size, and coating on the solid particles. A
mixture being essentially free of a dye relates to a dye
concentration of less than 0.001 vol %. In contrast, radiation
curable mixtures which do not contain solid particles and are fully
polymer-based, generally require a dye in order to control unwanted
photopolymerization.
[0092] The total volume of the three-dimensional body created by
the process of the present disclosure can be at least 0.1 mm.sup.3,
such as at least 0.3 mm.sup.3, at least 0.5 mm.sup.3 or at least 1
mm.sup.3. If the process of the present disclosure employs a
replenishable reservoir, as shown in FIG. 1, the method may not
have a specific upper limit of the total volume of the formed
three-dimensional body. For example, in one embodiment,
interconnected parts can be formed and directly fed into a furnish,
whereby no specific upper limit of the body volume may exist.
[0093] The method of the present disclosure can be further
characterized by producing three-dimensional bodies from mixtures
having a high content of solid particles, whereby the formed bodies
can have an exceptional uniform structure, high strength and high
smoothness.
[0094] In one embodiment, the method of the present disclosure is
characterized that a three-dimensional body including ceramic
particles can be continuously manufactured at a high production
speed. In one aspect, the creating of the three dimensional body
can be completed at a speed rate of at least 25 mm/hr, such as at
least 30 mm/hr, at least 40 mm/hr, at least 50 mm/hr, or at least
70 mm/hr.
[0095] In a particular embodiment, the three dimensional body of
the present disclosure can be subjected to high temperature
sintering to remove the radiation curable material and to form a
sintered body. If the solid particles of three dimensional body
subjected to high temperature sintering are ceramic particles, the
sintered body is called hereafter a ceramic body.
[0096] The sintering temperature can be at least 900.degree. C.,
such as at least 950.degree. C., at least 1000.degree. C., at least
1050.degree. C., at least 1100.degree. C., or at least 1150.degree.
C. In other aspects, the sintering temperature can be not greater
than 1600.degree. C., such as not greater than 1550.degree. C., not
greater than 1500.degree. C., or not greater than 1400.degree. C.
It will be appreciated that the sintering temperature can be a
value between any of the minimum and maximum values noted above,
such as from 900.degree. C. to 1600.degree. C., from 1000.degree.
C. to 1500.degree. C., or from 1100.degree. C. to 1350.degree.
C.
[0097] In a certain embodiment, the high temperature sintering can
lead to a ceramic body having a density of at least 90% of its
theoretical density.
[0098] In particular embodiments, the ceramic body can consist
essentially of ceramic particles. In one aspect the ceramic body
may consist essentially of alumina. In another aspect, the ceramic
body can consist essentially of silica. Consisting essentially of
ceramic particles means that the ceramic body comprises at least 99
wt % ceramic particles based on the total weight of the ceramic
body.
[0099] Many different aspects and embodiments are possible. Some of
those aspects and embodiments are described herein. After reading
this specification, skilled artisans will appreciate that those
aspects and embodiments are only illustrative and do not limit the
scope of the present invention. Embodiments may be in accordance
with any one or more of the embodiments as listed below.
EMBODIMENTS
Embodiment 1
[0100] A method of forming a body comprising:
[0101] forming a three-dimensional body from a mixture, the mixture
comprising at least 15 vol % of solid particles for a total volume
of the mixture and a radiation-curable material, wherein forming
includes continuous translation and growth of the body from an
interface of the mixture.
Embodiment 2
[0102] A method of forming a body comprising:
[0103] providing an assembly including a chamber containing a
mixture and a construction;
[0104] forming a three-dimensional body by continuously creating
and attaching a radiation cured translating portion to a carrier
plate of the construction and increasing a distance between the
carrier plate and the mixture in a continuous manner to create a
three-dimensional body within the mixture, wherein during forming
the three-dimensional body is adjacent to an interface of an
inhibition zone of the mixture,
[0105] wherein the mixture comprises a liquid characteristic
selected from the group of:
[0106] a shear-thinning slurry;
[0107] a shear-thinning slurry with a radiation-curable
material;
[0108] a content of solid particles of at least 15 vol % for a
total volume of the mixture;
[0109] a yield point of less than 10 Pa;
[0110] a viscosity of at least 50 cP at a shear rate of less than
about 5 Hz, and a viscosity of less than 1000 cP at a shear rate
greater than about 25 Hz;
[0111] or a combination thereof.
Embodiment 3
[0112] The method of embodiments 1 or 2, wherein the
radiation-curable material comprises a photoinitiator and a
polymerizable monomer.
Embodiment 4
[0113] The method of any of embodiments 1 to 3, wherein during
forming portions of the mixture are subjected to electromagnetic
radiation having a wavelength in a range from 200 nm to 760 nm.
Embodiment 5
[0114] The method of embodiment 4, wherein the electromagnetic
radiation has a wavelength within a range from at least 370 nm to
not greater than 450 nm.
Embodiment 6
[0115] The method of embodiments 4 or 5, wherein the
electromagnetic radiation has an energy within a range from at
least 20 mJ/cm2 to not greater than 450 mJ/cm2.
Embodiment 7
[0116] The method of embodiment 6, wherein the electromagnetic
radiation has an energy within a range from at least 20 mJ/cm2 to
not greater than 200 mJ/cm2.
Embodiment 8
[0117] The method of embodiment 7, wherein the electromagnetic
radiation has an energy within a range from 20 mJ/cm2 to 100
mJ/cm2.
Embodiment 9
[0118] The method of embodiment 3, wherein the photoinitiator
comprises a free-radical photoinitiator.
Embodiment 10
[0119] The method of embodiment 3, wherein the polymerizable
monomer comprises a material selected from the group of acrylates,
acrylamides, urethanes, dienes, or a combination thereof.
Embodiment 11
[0120] The method of any of the previous embodiments, wherein the
solid particles include ceramic particles, metallic particles,
polymeric particles, or any combination thereof.
Embodiment 12
[0121] The method of embodiment 11, wherein the ceramic particles
comprise at least one material selected from the group of an oxide,
a carbide, a boride, a nitride, a silicide or a combination
thereof.
Embodiment 13
[0122] The method of embodiment 12, wherein the ceramic particles
comprise at least one material selected from the group of alumina,
ceria, zirconia, silica, magnesium-magnesia aluminate (MMA),
magnesia, silicon carbide, hydroxyapatite, cordierite, or a
combination thereof.
Embodiment 14
[0123] The method of any of embodiment 13, wherein the mixture
comprises solid particles selected from the group of alumina,
silica, MMA, or zirconia.
Embodiment 15
[0124] The method of any of the previous embodiments, wherein at
least a portion of the solid particles include a coating overlying
an exterior surface.
Embodiment 16
[0125] The method of embodiment 15, wherein the coated solid
particles provide a 50% lower scattering of an applied
electromagnetic radiation than corresponding uncoated
particles.
Embodiment 17
[0126] The method of embodiment 16, wherein the coated solid
particles provide a 90% lower scattering of an applied
electromagnetic radiation than the corresponding uncoated
particles.
Embodiment 18
[0127] The method of embodiment 15, wherein the coated solid
particles provide a 50% lower absorbance of an applied
electromagnetic radiation than corresponding uncoated
particles.
Embodiment 19
[0128] The method of embodiment 18, wherein the coated solid
particles provide a 90% lower absorbance of an applied
electromagnetic radiation than the corresponding uncoated
particles.
Embodiment 20
[0129] The method of any of the previous embodiments, wherein the
solid particles have an average particle size of at least 0.1 .mu.m
and not greater than 20 .mu.m.
Embodiment 21
[0130] The method of any of the previous embodiments, wherein the
solid particles have a multimodal particle size distribution.
Embodiment 22
[0131] The method of any of the previous embodiments, wherein the
solid particles have a particle size distribution comprising a
value of function (d50-d10)/d50 of less than 0.8.
Embodiment 23
[0132] The method of any of the previous embodiments, wherein the
solid particles have a particle size distribution comprising a
value of function (d90-d50)/d50 of less than 1.0.
Embodiment 24
[0133] The method of embodiments 1 or 2, wherein the mixture
comprises an inhibition zone wherein the radiation curable material
does not cure if subjected to electromagnetic radiation.
Embodiment 25
[0134] The method of embodiment 24, wherein the inhibition zone has
a thickness of at least 0.5 .mu.m and not greater than 600
.mu.m.
Embodiment 26
[0135] The method of embodiments 24 or 25, wherein forming
comprises selecting solid particles having an average particle size
relative to a thickness of the inhibition zone.
Embodiment 27
[0136] The method of embodiments 24 or 25, wherein forming
comprises selecting a concentration of the solid particles in the
mixture relative to a thickness dimension of the inhibition
zone.
Embodiment 28
[0137] The method of embodiment 26, wherein the average particle
size of the solid particles is not greater than 25% of the
thickness of the inhibition zone.
Embodiment 29
[0138] The method of embodiment 28, wherein the average particle
size of the solid particles is not greater than 10% of the
thickness of the inhibition zone.
Embodiment 30
[0139] The method of embodiment 2, wherein the chamber further
comprises an oxygen-permeable layer.
Embodiment 31
[0140] The method of embodiments 1 or 2, wherein the mixture is
essentially free of a dye.
Embodiment 32
[0141] The method of any of embodiments 4 to 31, wherein the
applied electromagnetic radiation has a power of at least 0.1
mW/cm.sup.2, such as at least 0.5 mW/cm.sup.2, at least 1.0
mW/cm.sup.2, at least 2 mW/cm.sup.2, or at least 3 mW/cm.sup.2.
Embodiment 33
[0142] The method of any of embodiments 4 to 32, wherein the
applied electromagnetic radiation has a power not greater than 250
mW/cm.sup.2, such as not greater than 100 mW/cm.sup.2, not greater
than 50 mW/cm.sup.2, or not greater than 10 mW/cm.sup.2.
Embodiment 34
[0143] The method of any of the precedent embodiments, wherein the
mixture is a shear thinning slurry.
Embodiment 35
[0144] The method of embodiment 34, wherein the shear thinning
slurry is characterized that a decrease in viscosity of the mixture
from a shear rate of 0.1 s.sup.-1 to a shear rate of 500 s.sup.-1
is at least 10 cP, such as at least 30 cP, at least 50 cP, or at
least 80 cP.
Embodiment 36
[0145] The method of embodiment 34, wherein shear thinning slurry
is characterized that a decrease in viscosity of the mixture from a
shear rate of 0.1 s.sup.-1 to a shear rate of 500 s.sup.-1 is not
greater than 1500 cP, such as not greater than 1200 cP, not greater
than 1000 cP, or not greater than 800 cP.
Embodiment 37
[0146] The method of any of the precedent embodiments, wherein the
mixture comprises alumina particles having an average particle size
from 100 nm to 5000 nm in an amount of 15 vol % to 50 vol %.
Embodiment 38
[0147] The method of embodiment 37, wherein the alumina particles
have an average particle size from 300 nm to 3000 nm and are
present in an amount of 18 vol % to 40 vol %, and wherein the
mixture is a shear thinning slurry having a viscosity of not
greater than 900 cP at a shear rate of 1 s.sup.-1, and at viscosity
of at least 70 cP at a shear rate of 500 s-1.
Embodiment 39
[0148] The method of embodiments 37 or 38, wherein the mixture has
a viscosity not greater than 150 cP at a shear rate of 500
s.sup.-1.
Embodiment 40
[0149] The method of any of embodiments 37 to 39, wherein the
mixture comprises at least 30 vol % alumina and the forming of the
three dimensional body is conducted at an applied UV power of at
least 3 mW/cm.sup.2 and not greater than 12 mW/cm.sup.2.
Embodiment 41
[0150] The method of any of embodiment 37 to 39, wherein the
alumina particles are present in an amount of 16 vol % to 25 vol %,
and the forming of the three dimensional body is conducted at an
applied UV power of at least 1.0 mW/cm.sup.2 and not greater than
12 mW/cm.sup.2.
Embodiment 42
[0151] The method of any of embodiments 1 to 36, wherein the
mixture comprises silica particles having an average particle size
from 100 nm to 5000 nm and in an amount of 15 to 40 vol %.
Embodiment 43
[0152] The method of embodiment 42, wherein the silica particles
have an average particle size from 1000 nm to 3000 nm and are
present in an amount of 25 vol % to 35 vol %, and wherein the
mixture is a shear thinning mixture having a viscosity of not
greater than 200 cP at a shear rate of 1 s.sup.-1 and a viscosity
of at least 50 cP at a shear rate of 500 s.sup.-1.
Embodiment 44
[0153] The method of embodiments 42 or 43, wherein the mixture has
a viscosity not greater than 100 cP at a shear rate of 500
s.sup.-1.
Embodiment 45
[0154] The method of any of embodiments 42 to 44, wherein the
mixture comprises at least 25 vol % silica and the forming of the
three dimensional body is conducted at an applied UV power of at
least 1.0 mW/cm.sup.2 and not greater than 12 mW/cm.sup.2.
Embodiment 46
[0155] The method of any of the precedent embodiments, further
comprising subjecting the three dimensional body to high
temperature sintering at a temperature of at least 1000.degree.
C.
Embodiment 47
[0156] The method of embodiment 46, wherein high temperature
sintering forms a ceramic body, the ceramic body having a density
of at least 90% of its theoretical density.
Embodiment 48
[0157] The method of embodiment 47, wherein the ceramic body
consists essentially of alumina.
Embodiment 49
[0158] The method of embodiment 47, wherein the ceramic body
consists essentially of silica.
Embodiment 50
[0159] The method of any of the precedent embodiments, wherein
forming is conducted at a forming speed of at least 25 mm/hr.
Embodiment 51
[0160] The method of any of the precedent embodiments, wherein
forming is conducted at a forming speed of at least 60 mm/hr.
Embodiment 52
[0161] A method of forming a body comprising: forming a
three-dimensional body using an additive manufacturing process, the
three-dimensional body having a content of ceramic solid particles
of at least 15 vol % for a total volume of the body, wherein the
three-dimensional body has a total volume of at least 0.1 mm.sup.3,
and wherein forming is completed at a forming speed of at least 25
mm/hr.
Embodiment 53
[0162] The method of embodiment 52, wherein the forming speed is at
least 60 mm/hr.
Examples
[0163] The following non-limiting examples illustrate the present
invention.
Example 1
[0164] Example 1 demonstrates the change in cure depth of
UV-radiation curable mixtures with different types of ceramic
particles. The ceramic particle powders used in the experiments
were alumina, zirconia, silica, magnesium-magnesia aluminate (MMA),
silicon nitride, silicon carbide, and graphite.
[0165] Ceramic slurries were prepared for each type of ceramic
powder using as radiation curable material for all samples 1,6
hexanediol diacrylate (Sartomer SR238, hereinafter used as
"monomer") and a photoinitiator (Irgacure 819). A summary of the
ceramic powder slurries used in the experiments can be seen in
Table 1.
TABLE-US-00001 TABLE 1 Amount Amount of Type of Aver. Spec. of
solid solid Amount of Amount of Amount of solid particle surface
particles particles monomer photoinitiator dispersant particles
size area [vol %] [wt. %] [wt. %] [wt. %] [wt. %] E1 -- -- -- E2
Al.sub.2O.sub.3 500 nm 7 35 67.52 29.35 0.59 2.55 E3 ZrO.sub.2 300
nm 7 27.6 69.09 27.14 0.54 3.23 E4 SiO.sub.2 1.7 .mu.m 2 30 51.49
45.79 0.91 1.81 E5 MMA 3 .mu.m 1 28 57.89 38.11 0.76 3.23 E6
Si.sub.3N.sub.4 1.5 .mu.m 9 27.4 55.88 37.99 0.76 5.37 E7 SiC 2
.mu.m 0.47 30 56.91 41.78 0.83 0.47
[0166] All mixtures E2 to E7 contained a dispersant which insured
that the ceramic particles did not settle over a time period of at
least 1 hour. Table 2 gives a summary of the settling tests
performed to select the appropriate dispersant. Three dispersants
(Disperbyk-111, Disperbyk-180, Disperbyk-168) were selected on the
basis of their potential chemical affinity to the radiation curable
monomer. Mixtures of monomer, specific dispersant and powder were
prepared and mixed using a resodyn acoustic mixer and were observed
thereafter for settling behavior over the period of four days. The
efficiency of each dispersant was assessed by visual inspection.
Disperbyk-111 was observed to be the most effective dispersant for
the alumina slurries, whereas Dysperbyk-168 was the best dispersant
for all the other mixtures.
TABLE-US-00002 TABLE 2 Type of Dispersant Disperbyk-168
Disperbyk-180 Solution of a high Alkylol molecular weight
Disperbyk-111 ammonium salt of block copolymer Copolymer with a
copolymer with with pigment acidic groups acidic groups affine
groups Alumina effective partially effective partially effective
(Al.sub.2O.sub.3) Zirconia (ZrO.sub.2) partially effective
effective effective Silicon Carbide not performed fully settled
effective (SiC) Silicon nitride not performed not effective
partially effective (Si.sub.3N.sub.4) MMA partially effective
partially effective effective (Magnesia- Magnesium Aluminate)
[0167] For the measurement of the cure depth, a chamber was filled
with the mixture to be tested (E1 to E7), and the mixture was
exposed to a static image made of a series of light dots, wherein
the dots differed in their light intensity. The image was projected
from a Digital Light Projector connected to a UV lamp (405 nm). The
light intensity of each dot was controlled by scaling down the [R G
B] intensity of the dots directly on the image. For most curing
experiments, the power of the lamp was 30 mW/cm.sup.2, and the
resin was exposed to the radiation for 60 seconds at a maximum UV
exposure of 1800 mJ/cm.sup.2 for the dot with the highest light
intensity. The thickness of each printed dot was then measured with
a micro-caliper to obtain a relationship of cure depth in
dependency to the UV exposure.
[0168] As can be seen in Table 3 and FIG. 3, the presence of
ceramic particles (samples E2 to E7) resulted in a much lower cure
depth in comparison to the cure depth of the mixture containing no
ceramic particles (E1). It can be further seen that there are large
differences between the tested mixtures. The highest cure depth was
observed for the silica comprising slurries, followed by slurries
containing MMA, alumina, zirconia and silicon carbide.
TABLE-US-00003 TABLE 3 Cure depth with varying UV exposure for
different mixtures UV Exposure Cure depth [.mu.m] [mJ/cm2] E1 E2 E3
E4 E5 E6 E7 247 800 140 66 608 269 -- -- 388 940 160 86 695 327 40
-- 529 900 180 86 770 322 -- -- 671 1010 190 94 803 349 -- -- 812
980 200 98 847 354 -- -- 953 1190 210 105 878 376 50 -- 1094 1210
210 111 898 389 -- -- 1235 1210 220 111 927 398 -- -- 1376 1280 230
116 958 414 -- -- 1518 1430 230 118 949 436 -- -- 1659 1420 240 120
1000 443 -- -- 1800 1320 250 125 1022 439 59 -- 2700 -- -- -- -- --
60 <1 3600 -- -- -- -- -- 66 -- 5400 -- -- -- -- -- 70 1
[0169] It can be further seen from FIG. 3 that the increase in cure
depth is linear to the logarithms of the applied radiation energy
for all mixtures. The slope of the straight lines for each mixture
can be correlated to the curing sensitivity D.sub.p of the mixtures
with regard to UV exposure.
[0170] Table 4 shows the curing sensitivity D.sub.p values obtained
from the slopes of FIG. 3 with regard to the refractive index of
the ceramic materials of the mixtures. Not to be bound by theory,
the sensitivity values D.sub.p indicate that the curing sensitivity
of the mixtures decreases with increasing scattering of the
particles and strongly relates to the refractive index of the
ceramic particles.
TABLE-US-00004 TABLE 4 Sensitivity Particle Exam- Ceramic D.sub.p
Refractive Particle Amount ple Particles [.mu.m] Index Size [vol %]
SSA E1 -- 249 1.5* E4 Silica 192 1.5.sup..dagger-dbl. 1700 nm 30 2
E3 MMA 85 1.7.sup..dagger-dbl. 3000 nm 28 <1 E2 Alumina 49
1.8.sup..dagger-dbl. 500 nm 35 7 E5 Zirconia 29
2.2.sup..dagger-dbl. 300 nm 27.6 7 *Monomer
.sup..dagger-dbl.Ceramic particles
Example 2
[0171] Radiation curable mixtures with and without Al.sub.2O.sub.3
(E4 and E1), have been further compared by measuring the thickness
of the inhibition zone for each sample with increasing UV
exposure.
[0172] As can be seen in Table 5 and FIG. 4, the presence of 35 vol
% Al.sub.2O.sub.3 lowered the thickness of the inhibition zone to a
large extent in comparison to the thickness of the inhibition zone
of the mixture not containing Al.sub.2O.sub.3.
TABLE-US-00005 TABLE 5 UV-Exposure Inhibition Zone and STD
Inhibition Zone and STD [.mu.m] [mJ/cm2] [.mu.m] no alumina 35 vol
% Al2O3 65 54 (3.5) 26 (2) 130 41 (5) 11 (3) 195 33 (6) 2 (4) 260
21 (4) -- 325 13 (5) -- 390 9 (4) --
[0173] It could further be observed that the amount of ceramic
particles and the applied UV exposure needed to be carefully
balanced in order to create an inhibition zone which can prevent
adsorption of cured mixture on the bottom surface of the chamber.
At a UV-exposure at 260 mJ/cm.sup.2 or higher, the alumina
containing slurries did not establish a functioning inhibition
zone, and the radiation cured mixture was sticking to the bottom
surface of the micro-chamber.
Example 3
[0174] Two different types of oxygen permeable membranes--AF-2400X
and PMP--were compared regarding their influence on the thickness
of a formed inhibition zone under otherwise equal conditions.
AF-2400X is an oxygen permeable Teflon membrane made by Biogeneral,
and PMP is a polymethylpentene based membrane, also called TPX,
made by MITSUI Chemicals. Both membranes had a thickness of 2.2
mils.
[0175] For the experiments, the radiation curable material of
Example 1 (CLEAR from Formlabs) was used without the inclusion of
Al.sub.2O.sub.3. As can be seen in Table 6, in the presence of the
AF-2400X membrane, the formed inhibition zone is much larger than
the inhibition zone created when using a PMP membrane. This
indicates that AF-2400X allows the penetration of higher amounts of
oxygen in comparison to PMP membrane.
TABLE-US-00006 TABLE 6 Thickness of Inhibition Thickness of
Inhibition Zone UV-Exposure Zone and STD [.mu.m] and STD [.mu.m]
[mJ/cm2] PMP AF-2400X 64.9 24 (7) 54 (3.5) 129.8 22 (4.5) 41 (5)
194.8 10 (4.5) 33 (6) 259.7 7 (5) 21 (4)
Example 4
[0176] Continuous forming of a three-dimensional body comprising
Al.sub.2O.sub.3
[0177] A mixture was prepared containing 20 vol % Al.sub.2O.sub.3
(Almatis A16) (equals 48.1 wt % Al.sub.2O.sub.3), 27.8 wt %
radiation curable monomer (Sartomer SR 238), 20.6 wt % radiation
curable oligomer (Formlab resin clear), 0.22 wt % of a photo
initiator (Irgacure 819), and 3.2 wt % dispersant
(Disperbyk-111).
[0178] The mixture was placed in a chamber of an assembly having a
similar design as shown in FIGS. 1A and 1B. The transparent window
of the chamber was made of oxygen permeable Teflon (AF-2400X) with
a thickness of 2.2 mils. As electromagnetic radiation unit was used
a lensed UV LED device including an array of 12 UV LEDs, each LED
having a maximum optical power of 5.6 Watt and a UV wavelength
maximum at 405 nm, and positioned below the transparent window of
the chamber. On the outer surface of the transparent window was
placed a mask having a round opening with a 3 mm inner
diameter.
[0179] A carrier plate attached to a vertically movable
construction was placed into the mixture of the chamber at a
distance of about 10 .mu.m above the surface of the transparent
window. The mixture was radiated with the UV LEDs, and with a minor
time delay of about 1 to 2 seconds, the carrier plate was started
to continuously move upwards, pulling a rod-shaped body out of the
mixture. The experiment was repeatedly conducted at different
continuous forming speeds, such as 30 mm/hour, 60 mm/hour, and 90
mm/hour, as well as at different UV exposures (see Table 7).
TABLE-US-00007 TABLE 7 Forming Speed UV Power [mm/hour]
[mW/cm.sup.2] 30 1.12 60 1.12 90 0.56
[0180] A picture of the rod-shaped body formed at a speed of 1.5
mm/min and a UV power of 0.56 mW/cm.sup.2 is shown in FIG. 6. A
comparison of the formed three-dimensional bodies at different UV
exposure and different forming speeds can be seen in FIG. 7. The
best quality could be obtained at the highest forming speed of 90
mm/hour and the lower UV power of 0.56 mW/cm.sup.2.
Example 5
[0181] A mixture was prepared with the same components as in
Example 4, but by increasing the amount of Al.sub.2O.sub.3 to 35
vol % (corresponding to 66.1 wt %). The exact formulation was as
follows: 66.61 wt % Al.sub.2O.sub.3 (A16 Almatis), 17.52 wt %
radiation curable monomer (Sartomer SR 238), 13.07 wt % radiation
curable oligomer (Formlab resin clear), 0.29 wt % of a photo
initiator (Irgacure 819), and 2.52 wt % dispersant (Disperbyk-111).
The mixture was not printable because of a too high viscosity. One
reason for the high viscosity was the high initial viscosity of the
radiation curable oligomer (Formlab resin clear). Based thereon,
for the further experiments with mixtures of high solid content
(above 25 vol %), no oligomer component was included into the
compositions.
Example 6
[0182] Continuous forming of three-dimensional body comprising
Al.sub.2O.sub.3 at different light intensities.
[0183] A mixture containing 35 vol % Al.sub.2O.sub.3 (Almatis A16)
was prepared according to the composition as shown in Table 1,
mixture E2.
[0184] A three dimensional body was formed according to the same
method and system as described in Example 4. The body was formed at
a speed of 60 mm/hour, but at two different applied UV intensities:
1.76 mW/cm.sup.2 and 7.06 mW/cm.sup.2. As can be seen in FIG. 8A,
at a UV power of 7.06 mW/cm.sup.2, a dense cylinder could be formed
with a desired smooth outer surface. In contrast, at the lower
applied UV power, the quality of the formed cylinder was not
satisfying, showing hollowed out portions and portions which were
not fully cured (FIG. 8B).
Example 7
[0185] Continuous forming of three-dimensional body comprising
silica at different light intensities.
[0186] A mixture containing 30 vol % silica was prepared according
to the composition shown in Table 1, mixture E4.
[0187] A three dimensional body was formed according to the same
method and system as described in Example 4. The body was formed at
a speed of 60 mm/hour, and at two different applied UV intensities:
1.76 mW/cm.sup.2 and 7.06 mW/cm.sup.2. Cylinders of high quality at
both UV powers could be formed (see FIG. 9). The forming results
correspond well with the previously measured high sensitivity
D.sub.p of the silica comprising mixture (see E4 of Example 1).
Example 8
[0188] Continuous forming of three-dimensional body comprising MMA
at different light intensities
[0189] A mixture containing 28 vol % MMA was prepared according to
the composition shown in Table 1, mixture E5.
[0190] A three dimensional body was formed according to the same
method and system as described in Example 4. The body was formed at
a speed of 60 mm/hour, and at two different applied UV intensities:
3.53 mW/cm.sup.2 and 7.06 mW/cm.sup.2. As can be seen in FIG. 10A,
a high quality cylinder could be formed at UV power of 3.53
mW/cm.sup.2. However, at a power of 7.06 mW/cm.sup.2, the formed
cylinder contained undesired ridges, see FIG. 10B. These ridges are
attributed to a periodic sticking of the formed body to the oxygen
permeable membrane caused by an excess of curing energy, which
hinders the forming of a functioning inhibition zone (see Example
2).
Example 9
[0191] Continuous forming of three-dimensional body comprising
zirconia with varying light intensity
[0192] A mixture containing 27.6 vol % zirconia was prepared
according to the composition shown in Table 1, mixture E3.
[0193] A three dimensional body was formed according to the same
method and system as described in Example 4. The body was formed at
a speed of 60 mm/hour, and at two different applied UV intensities:
7.06 mW/cm2 and 11.76 mW/cm.sup.2. As can be seen in FIG. 11, a
high quality cylinder could be formed at a UV power of 7.06
mW/cm.sup.2. At a power of 11.76 mW/cm.sup.2, however, a proper
forming of a body was not possible because the body was sticking to
the bottom of the chamber. The applied UV power was too high in
order to create a functioning inhibition zone.
[0194] Table 8: Summary of Examples 4 to 9: Continuous forming of
three-dimensional bodies at a forming speed of 60 mm/hour with
different types of ceramic particles and different light
intensities
TABLE-US-00008 TABLE 8 Applied UV power Type of Amount Example
[mW/cm.sup.2] Ceramic [vol %] Quality of formed body 4 1.12 Alumina
20 high quality 6 1.76 Alumina 35 low quality/hollowed portions 7
1.76 Silica 30 high quality 8 3.53 MMA 28 high quality 6 7.06
Alumina 35 high quality 7 7.06 Silica 30 high quality 8 7.06 MMA 28
low quality, undesired ridges 9 7.06 Zirconia 27.6 high quality 9
11.76 Zirconia 27.6 no forming possible, sticking to bottom of
chamber
Example 10
[0195] Continuous forming of three-dimensional bodies comprising
silica with different amounts of silica in mixtures.
[0196] Three mixtures were prepared with varying amounts of silica
in the mixtures: 30 vol % (E8), 40.3 vol % (E9) and 45.2 vol %
(E10). The average silica particle size in all three mixtures was
1.7 .mu.m. All mixtures further contained monomer (Sartomer SR238),
photoinitiator (Irgacure 819), and dispersant Dysperbyk-168).
[0197] Similar as in Example 1, the cure depths of the mixtures E8,
E9, and E10 were measured with increasing UV exposure and the
curing sensitivity D.sub.p for each mixture were calculated from
the slope of the linear curves (see FIG. 12). As can be seen in
FIG. 12, the slopes for all tested mixtures are very similar, which
indicates that the curing sensitivities D.sub.p of the mixtures
varied only minor with the changing amounts of solid loadings,
i.e., being 508 .mu.m (for E8), 489 .mu.m (for E9), and 371 .mu.m
(for E10).
[0198] As another characterization of mixtures E8, E9, and E10, the
viscosities with varying shear rate were measured for of each
mixture.
[0199] All viscosity measurements of the mixtures of the present
disclosure under certain shear rates were conducted with a
Discovery HR-1 Rotational Rheometer using a cone and plate geometry
with a 40 mm diameter and a 2 degree cone angle, wherein the shear
rate was constant across the entire sample. The tests were done in
flow mode at a temperature of 25.degree. C.
[0200] As can be seen in FIG. 13, mixture E8 showed a shear
thinning behavior, while mixtures E9 and E10 showed a shear
thickening behavior.
[0201] Three dimensional bodies were formed from mixtures E8, E9,
and E10 according to the same method and system as described in
Example 4. The bodies were formed at a speed of 60 mm/hour, and at
a UV intensity of 7.06 mW/cm2. As can be seen in FIG. 14, a high
quality cylinder was formed from mixture E8, however, cylinders
with inferior quality were formed with mixtures E9 and E10, which
included hollow parts. A summary of the experiments is shown in
Table 9.
[0202] Not to be bound to theory, the quality differences between
the formed bodies of mixtures E8, E9, and E10 indicate that
advantageous for the forming of a high quality body is a shear
thinning behavior of the mixtures.
TABLE-US-00009 TABLE 9 Viscosity Viscosity Type of Amount Amount
[cP] [cP] solid of SiO.sub.2 of SiO.sub.2 at shear rate at shear
rate Viscosity Quality of particles [vol %] [wt. %] 1 s.sup.-1 100
s.sup.-1 behavior printed body E8 SiO.sub.2 30 51.49 70 40 shear
high quality thinning E9 SiO.sub.2 40.3 64.15 150 150 shear
inferior thickening quality E1 SiO.sub.2 45.2 68.62 490 900 shear
inferior thickening quality
Example 11
[0203] Continuous forming of three-dimensional bodies comprising
alumina with different average particle size.
[0204] Three mixtures were prepared containing alumina particles in
an amount of 35 vol % but with varying average particle size, i.e.,
500 nm (mixture E11), 2 .mu.m (mixture E12), and 10 .mu.m (mixture
E13). All mixtures further contained monomer (Sartomer SR238),
photoinitiator (Irgacure 819), and dispersant Dysperbyk-111).
[0205] For evaluating printability of the mixtures, the cure depth
in dependency to the UV exposure (405 nm) was measured and the
sensitivity D.sub.p calculated from the slopes of the curves, as
described in Example 1. As can be seen in FIG. 15 and Table 10,
mixture E13 with the largest particle size had the highest curing
sensitivity.
[0206] Although mixture E13 had the highest sensitivity, its
viscosity behavior made it unsuitable for printing a body. The
viscosity measurement are shown in FIG. 15: Mixture E11 showed a
shear thinning behavior, and slurry E12 showed an almost Newtonian
behavior with a very low viscosity. In contrast, slurry E13 had a
high viscosity at low shear rates and showed chaotic measurements
over a larger viscosity range. Mixture E13 also showed a very rapid
settling behavior (within a few minutes).
[0207] As a result, continuous printing was not possible for
mixture E13. In comparison, both mixtures E11 and E12 were suitable
for printing, and cylindrical bodies with good quality were printed
at a forming speed of 60 mm/hour and a UV intensity of 7.06
mW/cm.sup.2. A summary of the results of Example 11 can be seen in
Table 10.
TABLE-US-00010 TABLE 10 Viscosity Viscosity Type of Aver. [cP] [cP]
solid particle Sensitivity at shear rate at shear rate Viscosity
Quality of particles size Dp 1 s.sup.-1 500 s.sup.-1 behavior
printed body E11 Al.sub.2O.sub.3 500 nm 87 700 95 shear high
thinning quality E12 Al.sub.2O.sub.3 2 .mu.m 121 85 90 Newtonian
high quality E13 Al.sub.2O.sub.3 10 .mu.m 271 n.d. 250 chaotic body
behavior at cannot be low shear formed rates; no shear thinning
Example 12
[0208] Forming a complex flower shape with alumina comprising
slurry followed by de-binding and sintering
[0209] A three dimensional flower-shaped green body was formed
using the same mixture and method as described in Example 2
(alumina comprising mixture, E2) The flower-shaped body was formed
at a speed of 60 mm/hour, and an applied UV intensity of 6
mW/cm.sup.2 (see FIG. 17).
[0210] After the forming of the green body, the following
de-binding and sintering regime was applied:
[0211] Heating at a rate of 1.degree. C./min up to 325.degree. C.;
holding the temperature for 30 minutes at 325.degree. C., heating
at rate of 1.degree. C./min up to 650.degree. C.; holding the
temperature for 1 hour at 650.degree. C.; heating at a rate of
5.degree. C./min up to 1480.degree. C.; holding the temperature for
30 minutes at 1480.degree. C.; heating at a rate of 1.degree.
C./min up to 1550.degree. C.; holding the temperature for 1 hour at
1550.degree. C.; cooling down at a rate of 5.degree. C./min to room
temperature.
[0212] After the high temperature sintering, the flower-shaped body
have kept its integrity, despite a shrinkage of about 23%. FIG. 17A
shows an example of a flower-shaped green body before high
temperature sintering, and FIG. 17B shows flower-shaped ceramic
bodies after high temperature sintering
[0213] The microstructure of the sintered ceramic flower was
investigated using Scanning Electron Microscope (SEM) technology.
Apart of a few minor surface delaminations, no larger cracks or
defects could be observed. Cross-sections of individual posts of
the flower were polished and thermally etched at 50.degree. C.
below the maximal sintering temperature for 30 minutes. As can be
seen in FIG. 18, the cross-section shows a high and uniform density
throughout the part with a grain size in the range of 0.5 to 10
microns.
[0214] The high density of the sintered ceramic flower was also
confirmed by Archimedes and Helium picnometry methods. The average
density was 92.7% of the theoretical density of alumina if measured
by the Archimedes method, and 93% of the theoretical density was
measured with the Helium pycnometry method.
[0215] In the foregoing specification, the concepts have been
described with reference to specific embodiments. However, one of
ordinary skill in the art appreciates that various modifications
and changes can be made without departing from the scope of the
invention as set forth in the claims below. Accordingly, the
specification and figures are to be regarded in an illustrative
rather than a restrictive sense, and all such modifications are
intended to be included within the scope of the invention.
* * * * *